Linewidth Roughness (LWR) remains a difficult challenge in resist materials. In previous work we focused on showing how roughness Power Spectral Density (PSD) parameters were affected by aerial image and basic resist parameters such as diffusion. This highlighted the relationship between PSD(0) and correlation length in optimizing LWR. By measuring the unbiased PSDs with MetroLER we showed LWR measurements could be expressed as a ratio between the roughness PSD parameters. In this paper we show how LWR improvement can be achieved by several strategies that focus on both PSD(0) and correlation length and not a single LWR number.
Linewidth Roughness (LWR) remains a difficult challenge for improvement in all resist materials. In previous work we focused on the impact of key components of LWR by analyzing the Power Spectral Density (PSD) curves which can be obtained using Fractilia’s MetroLER computational software.  By measuring the unbiased PSD (with SEM image noise removed), accurate assessment of PSD(0) (the low-frequency limit of the PSD) and correlation length (the length scale of the transition from white to correlated noise) is possible. We showed there was an important relationship between ArF resist frequency components and LWR through lithographic process (before and after a resist trim step) as a function of resist formulation. In this paper we will study how key frequency components such as PSD(0) and correlation length change as we vary basic resist properties such as diffusion. The impact of aerial image on LWR and its frequency components will also be studied with particular attention to how correlation length affects LWR as feature size decreases. We will also look at the impact of diffusion or resist blur on PSD(0) as a function of aerial image Normalized Image Log-Slope (NILS). Understanding the relationship between PSD(0) and correlation length and how to manipulate these variables to minimize LWR for different features is crucial for more rapid LWR improvement at different nodes.
 Charlotte Cutler, et al., “Roughness power spectral density as a function of resist parameters and its impact through process,” Proc. SPIE 10587, Optical Microlithography XXXI, 1058707 (23 March 2018).
Linewidth roughness (LWR) remains a difficult challenge for improvement in all resist materials. In this paper, we intend to focus on the impact of key components of LWR by analyzing the Power Spectral Density (PSD) curves which can be obtained using Fractilia’s MetroLER computational software. We will study systematic changes to ArF resist formulations and correlate these changes to the overall PSD curves. In this manner, we can extract LER/LWR 3σ values as well as resist correlation length and the low/high-frequency roughness components. We will also investigate the relationship between PSD and LWR through lithographic/etch processing and demonstrate which components correspond with the largest impact. In order to achieve quality data over low and high frequency ranges we changed our standard metrology setup to capture longer lines. By making systematic changes to the ArF resists, we can determine the key impacts of various controllable resist factors on the PSD. Through systematic analysis, we can deconvolute LWR improvements both after develop and after an etch process.
A trilayer stack of spin-on-carbon (SOC), silicon anti-reflective coating (SiARC) and photoresist (PR) is often used to enable high resolution implant layers for integrated circuit manufacturing. Damage to substrates from SiARC removal using dry etching or aqueous hydrogen fluoride has increased the demand for innovative SiARC materials for implant lithography process. Wet strippable SiARCs (WS-SiARCs) capable of stripping under mild conditions such as SC1 (ammonium hydroxide/hydrogen peroxide/water) while maintaining key performance metrics of standard SiARCs is highly desirable. Minimizing the formation of Si-O-Si linkages by introducing organic crosslink sites was effective to impart SC1 solubility particularly after O2 dry etching. Incorporation of acidic groups onto the crosslinking site further improved SC1 solubility. A new siloxane polymer architecture that has SC1 active functionality in the polymer backbone was developed to further enhance SC1 solubility. A new SiARC formulation based on the new siloxane polymer achieved equivalent lithographic performances to a classic SiARC and SC1 strip rate >240Å/min under a relatively low concentration SC1 condition such as ammonium hydroxide/hydrogen peroxide/water=1/1/40.
As the critical dimension of devices is approaching the resolution limit of 193nm photo lithography, multiple patterning processes have been developed to print smaller CD and pitch. Multiple patterning and other advanced lithographic processes often require the formation of isolated features such as lines or posts by direct lithographic printing. The formation of isolated features with an acceptable process window, however, can pose a challenge as a result of poor aerial image contrast at defocus. Herein we report a novel Chemical Trimming Overcoat (CTO) as an extra step after lithography that allows us to achieve smaller feature size and better process window.
With the continuous demand for higher performance of computer chips and memories, device patterns and structures are becoming smaller and more complicated. Hard mask processes have been implemented in various steps in the devise manufacturing, and requirements for those materials are versatile. In this paper, novel organometal materials are presented as a new class of spin on solution in order to support the hard mask process. Type of metals, formulation scheme and processing conditions were carefully designed to meet the fundamental requirements as a spin on solution, and their characteristic properties were investigated in comparison to other conventional films such as spin on carbons (SOC), organic bottom anti-reflective coatings (oBARC) and inorganic films formed by chemical vapor deposition (CVD). Several advantages were identified with these SOMHM materials over other films which include 1) better thermal stability than SOC once fully cured, 2) reworkable with industry standard wet chemistry such as SC-1 where conventional Si-BARC is difficult to remove, 3) a wide range of optical constants to suppress reflection for photoresist imaging, 4) high etch resistance and 5) better gap filling property. Curing conditions showed a significant impact on the performance of SOMHM films, and X-ray photoelectron spectroscopy (XPS) was utilized to elucidate the trends. With SOMHM film as a BARC, photolithographic imaging was demonstrated under ArF immersion conditions with 40nm linewidth patterning.
Understanding fundamental properties of photoresists and how interactions between photoresist components affect
performance targets are crucial to the continued success of photoresists. More specifically, polymer solubility is critical
to the overall performance capability of the photoresist formulation. While several theories describe polymer solvent
solubility, the most common industrially applied method is Hansen’s solubility parameters. Hansen’s method, based on
regular solution theory, describes a solute’s ability to dissolve in a solvent or solvent blend using four physical properties
determined experimentally through regression of solubility data in many known solvents. The four physical parameters
are dispersion, polarity, hydrogen bonding, and radius of interaction. Using these parameters a relative cohesive energy
difference (RED), which describes a polymer’s likelihood to dissolve in a given solvent blend, may be calculated.
Leveraging a high throughput workflow to prepare and analyze the thousands of samples necessary to calculate the
Hansen’s solubility parameters from many different methacrylate-based polymers, we compare the physical descriptors
to reveal a large range of polarities and hydrogen bonding. Further, we find that Hansen’s model correctly predicts the
soluble/insoluble state of 3-component solvent blends where the dispersion, polar, hydrogen-bonding, and radius of
interaction values were determined through regression of experimental values. These modeling capabilities have
allowed for optimization of the photoresist solubility from initial blending through application providing valuable
insights into the nature of photoresist.
The shot noise, line edge roughness (LER) and quantum efficiency of EUV interaction with seven resists related to EUV-2D (SP98248B) are studied. These resists were identical to EUV-2D except were prepared with seven levels of added base while keeping all other resist variables constant. These seven resists were patterned with EUV lithography, and LER was measured on 100-200 nm dense lines. Similarly, the resists were also imaged using DUV lithography and LER was determined for 300-500 nm dense lines. LER results for both wavelengths were plotted against Esize. Both curves show very similar LER behavior-the resists requiring low doses have poor LER, whereas the resists requiring high doses have good LER. One possible explanation for the observed LER response is that the added base improves LER by reacting with the photogenerated acid to control the lateral spread of acid, leading to better chemical contrast at the line edge.
An alternative explanation to the observed relationship between LER and Esize is that shot-noise generated LER decreases as the number of photons absorbed at the line edge increases. We present an analytical model for the influence of shot noise based on Poisson statistics that preidicts that the LER is proportional to (Esize)-1/2. Indeed, both sets of data give straight lines when plotted this way (DUV r2 = 0.94; EUV r2 = 0.97). We decided to further evaluate this interpretation by constructing a simulation model for shot noise resulting from exposure and acid diffusion at the mask edge. In order to acquire the data for this model, we used the base titration method developed by Szmanda et al. to determine C-parameters and hence the quantum efficiency for producing photogenerated acid. This information, together with film absorptivity, allows the calculation of number and location of acid molecules generated at the mask edgte by assuming a stochastic distribution of individual photons corresponding to the aerial image function. The edge "roughness" of the acid molecule distribution in the film at the mask edge is then simulated as a function of acid diffusion length and compared to the experimental data. In addition, comparisoins between of the number of acid molecules generated and photons consumed leads to values of quantum efficiencies for these EUV resists.
The relationships between polymer molecular weight, surface roughness measured by Atomic Force Microscopy (AFM), and EUV line edge roughness (LER), were studied in four separate rounds of experiments. In Round 1, EUV-2D (XP98248B) was prepared with seven levels of added base. These seven resists were patterned using EUV lithography; the LER was determined using 100 nm dense lines. The LER of the seven resist dramatically decreases with increasing level of base. These LER results were compared with the surface roughness of these resists after development for unexposed and DUV (248 nm) exposed surfaces. In Rounds 2-4, we evaluated three sets of EUV-2D type resists prepared with polymers having Mw of 2.9, 4.9, 6.1, 9.1, 16.1, and 33.5 Kg/mole. EUV LER and surface roughness were determined for each resist. In Round 2, the polymers were substituted into the EUV-2D resist matrix with no other formulation changes. In Round 3, the PAG level was decreased with increasing polymer Mw, to obtain a constant unexposed fill thickness loss (UFTL) for all six resists. In Round 4, both PAG level and base level were modified to yield six resists with similar sensitivity and EFTL. These experiments have led to conclusion about the impact of polymer molecular weight on imaging LER and AFM surface roughness, as well as elucidating the relationship between all three.